Function Code Substitutions - GE TRANSFORMER MANAGEMENT RELAY 745 Instruction Manual

7 COMMUNICATIONS
3. Setpoints may be written via the user map. In the example above, to change the value of Restrained Differential Pickup
to 0.20 x CT through the user map, transmit the following Modbus message:
MASTER QUERY MESSAGE:
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS: high order byte, low order byte
DATA: high order byte, low order byte
CRC: low order byte, high order byte
SLAVE RESPONSE:
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS: high order byte, low order byte
DATA: high order byte, low order byte
CRC: low order byte, high order byte
Most 745 supported Modbus commands can be performed via function codes 03h (or 04h), and 10h and special memory
map addresses.
a) FUNCTION CODES 03H AND 04H SUBSTITUTIONS
Function codes 03h and 04h are interchangeable. Both have identical message formats, and both perform the same action.
b) FUNCTION CODE 05H SUBSTITUTION
Function code 05h (Execute Operation) can be performed by writing the command as if it were data in the memory map.
For example, to write operation code 01h (reset targets) to register 0080h, the message format and example is shown
below.
Request slave device 11 to reset targets:
MASTER QUERY MESSAGE:
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS: high order byte, low order byte
NUMBER OF SETPOINTS: high order byte, low order byte
BYTE COUNT
DATA: high order byte, low order byte
CRC: low order byte, high order byte
SLAVE RESPONSE:
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS: high order byte, low order byte
NUMBER OF SETPOINTS: high order byte, low order byte
CRC: low order byte, high order byte
GE Multilin
Courtesy of NationalSwitchgear.com
EXAMPLE (HEX):
11 query message for slave 11
06 store single setpoint values
01 85 data starting at address 0185
0014 = 0.30 × I
00 14
9B 40 CRC computed by master
EXAMPLE (HEX):
11 response message from slave 11
06 store single setpoint values
01 85 data starting at address 0185
0014 = 0.30 × I
00 14
9B 40 CRC computed by slave
EXAMPLE (HEX):
11 query message for slave 11
10 store multiple setpoints (substituted for code 05H)
00 80 data starting at address 0080
00 01 1 register values = 2 bytes total
02 2 bytes of data
00 01 0001 = operation code 0001H (reset targets)
B5 90 CRC computed by master
EXAMPLE (HEX):
11 response message from slave 11
10 store multiple setpoints
00 80 data starting at address 0080
00 01 1 setpoint values = 2 bytes total
02 31 CRC computed by slave
745 Transformer Management Relay
7.3 MODBUS FUNCTIONS
d
d

7.3.6 FUNCTION CODE SUBSTITUTIONS

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